Catalyst: Toorale Man mystery - ABC TV Science

[baeckmo]

Interesting topic, and in fact also having a bearing on fluid mechanisms around a (high-speed) hull.

This kind of damage could well be explained by the pressure-wave propagation speed and the resulting "waterhammer" pressure. The grey matter inside the skull is a combination of fat (ie a semi-liquid substance) and blood (ie a fluid containing both solid and gaseous phases). It is not completely filling the bowl, but is surrounded by additional fluid.

First the basic physics: a momentary deflection/displacement of a fluid wall or part of the envelope, is propagating through the fluid at the speed of sound (the "critical propagation velocity, CPV") in the specific fluid. This velocity varies roughly between ~830 m/s and ~1900 m/s for common fluids (water at room temperature: ~1200 m/s) in a stiff pipe. If the containing walls are elastic (which they always are....), the critical velocity is reduced. In PVC, for instance you find the corresponding velocities reduced to between 230 and 380 m/s.

Now imagine that the fluid with CPV=300 m/s and density=900 kg/m3 is moving with a transport velocity A=45 m/s. If the transport velocity is suddenly stopped, you will get a pressure "spike" with a top pressure of:

P=900 x 45 x 300 =12,15 e6 Pascale, corresponding to about 122 bars;

This means that the fluid is extremely hard when there is a change in velocity; if the scull was moving towards the boomerang with 45 m/s (instead of vice versa), the pressure wave inside the bowl would "resist" deformation from the blow except close to the impact zone. The pressure-wave phenomenon makes for a very clean cut; it's like having a support with a narrow channel beneath the bone bowl. So, if the weapon is a hard wood boomerang, I'd say it is physically possible that it may result in a nice, clean cut, provided the impact velocity is high enough.

I'd guess this is also the mechanism making decapitating of bottles possible (not that I have been excelling in these stunts....), and it is the reason why slamming pressures in a planing hull can be reduced by hull shapes that generate "air foaming" along the bottom. It simply reduces the critical propagation velocity in the equation above.


Edit: I later read the report on bullets hitting a femur, and the discussion, where the authors speculated about "cavitation damage". That is sheer nonsense, they do not understand the dynamic procedures of cavitation or the "water-hammer" phenomenon.

 

[cutting edge]

baeckmo
Very interesting. If a weapon weighs about 1kg then a body of 80kg has some inertia . If the skull is locked into concrete and can't move then do we have a similar effect to CPV hammer of 122 bars? There is blood and marrow inside the skull bone , the cortex , which also has this resistant effect and which may have cavitation. Glass may shatter cleanly. However, steel balls or baseball bats cause collapsed bone , comminuted depression fractures . The fibrous trabeculae structure of bone is more ductile than the cortical layer giving a complex random breaking pattern compared with sharp cuts .

The skull collapsed at 4N for 8sq cm and at 8N for 4sq cm. Femur bone also collapsed at higher velocity with a 9mm ball. So the energy acts as Velocity Area . It may be like the sharpness of a bow and width of beam. Does water resistance / boat speed vary with area of bow section ( in basic terms) ?

 

[philSweet]

BTW Baeckmo, I was going to say something about that, but it turned out the speed of sound through skull bones has been measured (multiple times), and the published numbers were higher that what I wanted in order to make that argument. Of course, it is likely that the measured figure is just the leading edge from solid conductivity, and not the the applicable speed for fluid shock within the skull.

Further reading suggests burial in calcium rich Austrailian river sediment is about the worst possible situation for carbon dating. Diet alone could account for a 500 year variation in reported age. It's actually bit strange the sediment dates to the same age as the body. It was buried - the sediment should be older.

 

[Mr Efficiency]

All speculation really, a guessing game, what is known for sure is that aboriginal Australians have unusually thick skulls, probably a result of selective pressures from millenia of inter-tribal warfare, where weapons such as the nulla-nulla figured prominently.

 

[cutting edge]

philSweet
Just checking on this hammer effect : would the shock travel to the far side of the skull and damage that ? Head injuries usually show the impact only , what is the water-hammer doing in particular? This skull only has trauma on the external bone not internal. Wouldn't the effect be to increase general damage rather than allow a slicing cut? At about bullet speed a femur explodes .

500 years earlier is still before iron swords in Oz , 500 years later is before Capt Cook arrived.

." bone's structural strength comes from calcium hydroxyapatite, which is easily contaminated with carbonates from ground water. Removing the carbonates also destroys the calcium hydroxyapatite, and so it is usual to date bone using the remaining protein fraction after washing away the calcium hydroxyapatite and contaminating carbonates. This protein component is called collagen. Collagen is sometimes degraded, in which case it may be necessary to separate the proteins into individual amino acids and measure their respective ratios and 14 C activity. It is possible to detect if there has been any degradation of the sample by comparing the relative volume of each amino acid with the known profile for bone. If so, separating the amino acids may be necessary to allow independent testing of each one—agreement between the results of several different amino acids indicates that the dating is reliable. "

The sediment was from stones within a crayfish stomach.

A student did a thesis on the weapons of Aboriginals and failed to reproduce the trauma using pigskull , as I also failed . The 10mm wood just dents the bone without cutting where my blunt garden spade easily sliced in. Timber axemen sharpen their axes and surgeons use chisels 2mm thick to avoid side damage due to thicker impacts.

I'm curious why the Velocity.Area / Velocity sq Area is not being considered.

 

[cutting edge]

Mr Efficiency
Years of swords , maces , pole-axes , shrapnel and IED has made us thick skinned but hardly bone-headed.

 

[Mr Efficiency]

You don't get a selective advantage from anything that kills you, you get it from surviving what may well have killed, but for a particular trait you carry.

 

[cutting edge]

By JOHN ELIGON APRIL 3, 2008


A man in North Carolina was shot roughly 20 times in 1995 and lived to tell about it. The rapper 50 Cent was shot nine times in 2000 and has since released three albums. And in 2006, Joseph Guzman survived 19 gunshot wounds during the 50-shot fusillade by police detectives that killed Sean Bell.

While surviving numerous gunshots could be a miraculous feat, doctors who have treated gunshot victims say that being shot is not automatically a death sentence.

Mr. Guzman survived an onslaught that would kill a person 99 percent of the time, Dr. DiMaio said. Mr. Guzman’s saving grace may have been the Nissan Altima he sat in as the detectives fired, Dr. DiMaio said.

“If they go through metal, the bullets may have so little energy they get into the muscle or fat and then they stop,” he said.

 

[cutting edge]

Catalyst: Toorale Man murder mystery - ABC TV Science
www.abc.net.au/catalyst/stories/4211835.htm
.... on Toorale Man appear similar to those on gladiators in Imperial Rome.
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This arose from a thread in Hydrodynamics " angle resistance". It shows how the blade cut both the skull and eye bone . The side of the top and lower jaws were also sliced indicating a long weapon . It was in 1200s before guns and Indonesian kris swords were up to 60cm . A conquest was not the only option as not everyone was like Europeans and evidently the arrivals were welcomed like Macassan fishermen were in north Australia from 1500s. It seems the swordsmen brought Indonesian Hindu-Buddhism to east Australia and merged with the population.

Wood can't be sharpened like metal so the English started making bronze when Stonehenge was finished because they had sore knuckles from stone hammers. I tried sharp mulga wood on pigskull, like the author of the articles about the skull , and both of us failed to make an impression. Still , what's science got to do with it and if wood looks sharp then that's OK and it cuts bone. Surgeons may start using wooden chisels to cut bone . Maybe not.

An Aboriginal elder , Badger Bates, who found the skull says "Our old people back then did not have a blade like that. If that carbon date is 700 years old, there is something wrong somewhere."

 

[cutting edge]

Here is some background to Indonesia :

"The earliest evidence of the presence of Bajo in Sulawesi is the mention of a people called Bajo Sereng (Moluccan Bajo) in the major narrative epic from South Sulawesi — the La Galigo cycle (Pelras 1996: 74). This reference apparently relates to the role Bajo may have played in relations between the maritime powers of South Sulawesi and the Moluccas. According to Pelras, this text probably dates from the fourteenth century, at the time of the dominant kingdom of Luwu". ( Stacey. 2007: 10). Their voyages began in fourth century and later included sailing to Madagascar off Africa's coast. ( Ring, Salkan and La Boda. 1996).

The first king of Kediri in Java to leave historical records was Çāstaprabhu(1104–1115). In his inscription dated 1104, like predecessor Airlangga, he claimed himself to be the incarnation or Avatar of god Vishnu. King Kertajaya " judge. victory" (1200-1222) asked his Hindu and Buddhist priests to worship him as Shiva. They rebelled and Ken Arok attacked causing Kertajaya to "disappear without trace", " went to devalaya "land of gods" ".( Coedes 1968). Kertajaya's navy and merchant fleets had been sailing to west Papua. Ken Arok was murdered and succeeded by Kertanagara "judge. country" a Tantric Buddhist as was Kertajaya. (Whitten and Whitten 2005)..


According to a Chinese source in the book of Chu-fan-chi written around 1225, Chou Ju-kua described the Southeast Asian archipelago having two powerful and rich kingdoms: Srivijaya and Java (Kediri). The book mentioned that Java was ruled by a maharaja, who ruled several colonies including Tung-ki (Jenggi, West Papua) and Huang-ma-chu (Southwest Papua) . ( Soekmono 1988).

An inscription (dated 1181) documents Senapati Sarwwajala, or laksmana, a title reserved for navy generals,"commander of water matters" which may mean that Kediri had a navy . Kediri's expertise in ship-building was noted at that time and the Portuguese later wrote of the imposing Majapahit fleets.

 

[Mr Efficiency]

Your sword could have been trade goods, or forcibly acquired.......and found its way into the hinterland. Not sure what kind of animal fat might have been available to keep rust at bay, though !

 

[Mr Efficiency]

Like a dog with a bone, (skull in this case) Cutting Edge won't let go of this obsession !

 

[cutting edge]

But it seems you agree it may not be a boomerang. I just get cranky when experts talk rubbish and tell lies against their own facts . There was an Australia before 1770 and it was an interesting place with Buddhists hunting roos .

 

[Mr Efficiency]

Well, it cannot be discounted. Australia is too close to Asia to have been in isolation, you can deduce that the Aboriginal inhabitants were formidable protectors of their ground.

 

[gonzo]

cutting edge: The first humans to reach Australia traveled from a different continent. Why would they be the only to be able to do that? You seem to have the same attitude as the experts you criticize. Stone can be sharpened to cut very well; particularly igneous.